1. Field of the Invention
The present invention relates to a receiver which is capable of receiving both RDS (Radio Data System) or DARC (DAta Radio Channel) FM multiplex broadcasting signals.
2. Description of the Related Art
In FM multiplex-broadcasting, the RDS system is common in Europe, while the DARC system prevails in Japan.
A typical RDS signal demodulating circuit 1, such as shown in FIG. 2, is composed of a bandpass filter BPF 2 for passing only signal components in a band centering around 57 kHz of an RDS modulated signal received, a BPSK demodulator 3 for performing BPSK demodulation of an output signal of the bandpass filter BPF 2, an RDS synchronous regeneration circuit 4 for performing synchronous regeneration based on a demodulated signal, an RDS error correction circuit 5 for detecting errors of RDS data demodulated, correcting these errors, and outputting the corrected RDS data, and a crystal oscillator 7 which generates a reference clock RDSCL due to the connection with a crystal resonator 6. As the bit rate of an RDS signal is 1.1875 Kbps, a frequency of 4.332 MHz, or 3648 times the bit rate, is commonly used for the crystal resonator 6.
On the other hand, a typical DARC signal demodulating circuit 10, such as shown in FIG. 3, is composed of a bandpass filter BPF 12 for passing only a band centering around 76 kHz of a DARC modulated signal received, an MSK demodulator 13 for performing MSK demodulation of an output signal of the bandpass filter BRF 12, a DARC synchronous regeneration circuit 14 for performing synchronous regeneration based on the demodulated signal, a DARC error correction circuit 14 for detecting errors of DARC data demodulated, correcting them, and outputting the DARC data corrected, and a crystal oscillator 17 for generating reference clocks DARCCLs by the connection of a crystal resonator 16. Here, since the bit rate of a DARC signal is 16 Kbps, a frequency of 7.2 MHz, which is 450 times this bit rate, is generally used for the crystal resonator 16.
Thus, in order for a receiver to receive FM multiplex broadcasting of both the RDS and the DARC system, it is now necessary to install in the receiver both the RDS signal demodulating circuit 1 and the DARC signal demodulating circuit 10 which are shown in FIGS. 2 and 3, and two crystal resonators 6 and 16 for generating reference clocks.
Also, FM multiplex broadcasting using both the RDS and DARC systems in a single radio station is about to commence in Europe. Receivers having a constitution similar to the above will be required to listen to broadcasts from such a station.
As described above, in order for a receiver to receive FM multiplex broadcasting of both the RDS and the DARC systems, separate crystal resonators applicable to the respective systems are required along with separate demodulating circuits applicable to each system. A relatively large number of components of are therefore required for these circuits. Further, because the reference clock frequencies of the RDS and DARC systems differ (4.332 MHz vs. 7.2 MHz), it is difficult to simply use a single, common crystal resonator.
Further, if the demodulating circuit is converted into an LSI, the crystal resonators must still be externally installed. The number of external components therefore undesirably increases.